People are injecting gas into their eyelids to combat dark circles

Forget all those creams that promise to reduce eye puffiness. A new beauty trend makes your eyes swell up on purpose — with the goal of making you look less tired.

Fans of the procedure, called carboxytherapy, can spend thousands of dollars to have carbon dioxide injected both above and below the eye, hoping to stimulate blood flow and erase dark circles.

But experts caution there isn't any evidence to back up the procedure. It's likely not even targeting the real root of the skin blemishes. "I would be very skeptical of its use for dark circles," said Dr. Molly Wanner, a cosmetic dermatologist at Massachusetts General Hospital.

Here's how it claims to work: Carbon dioxide builds up in our cells naturally, and blood carries it away. Carboxytherapy injections are supposed to trick the area around the eye into thinking it needs more oxygen, which dilates blood vessels and stimulates increased blood flow in the area.

But that strategy is based on the theory that dark circles are caused by poor circulation, and that's not often the case, experts say. More commonly, dark circles show up because the skin under the eyes is thin, which makes the dark tint of blood vessels more visible.

A study published in Skin Research and Technology in 2015 found there was no difference in blood flow to the eye area between people with dark circles and people without.

That hasn't stopped clinics from offering the puffing procedure in the United States and abroad. Eye carboxytherapy can cost anywhere from $75 to upward of $200 a session, and some clinics urge patients to get as many as a dozen treatments. (The procedure is also marketed to treat stretch marks, even out cellulite, and improve the appearance of some scars.)

There aren't any documented cases of bad side effects from the eye treatments, but that doesn't mean it's completely safe, experts caution.

"It gives you gas in an area where it's not supposed to be," Wanner said. Bruising at the injection site is common.